The anus is the opening at the end of the digestive tract where stool leaves the body. The rectum is the section of the digestive tract above the anus where stool is held before it passes out of the body through the anus. The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine. The rectal lining consists of glistening red tissue containing mucus glands—much like the rest of the intestinal lining.
Chapter 36: The rectum and anal canal
Rectum, Anus, and Anal Sphincter
At the level of the middle of the sacrum, the sigmoid colon loses its mesentery and gradually becomes the rectum, which, at the upper limit of the pelvic diaphragm, ends in the anal canal fig. The rectum, about 15 cm long, widens below as the ampulla, which is very distensible. Although variable in shape, the rectum follows the sacrococcygeal curve. At the anorectal junction, the gut curves backward and its concavity is held by the puborectal sling, which can be palpated per anum.
Overview of the Anus and Rectum
The rectum is a muscular tube about 13 cm 5 in. The rectum connects the colon to the anus, which is the opening where stool exits the body. The internal and external anal sphincters are rings of muscle at the opening of the anus. The sphincters keep the anus closed as stool collects in the rectum.
The rectum is the final straight portion of the large intestine in humans and some other mammals , and the gut in others. The adult human rectum is about 12 centimetres 4. It terminates at the level of the anorectal ring the level of the puborectalis sling or the dentate line , again depending upon which definition is used. The word rectum comes from the Latin rectum intestinum , meaning straight intestine. The rectum is a part of the lower gastrointestinal tract.